This study used ultrasonography to measure fetal biparietal diameter and crown-rump length in Cheviot ewes in order to predict lambing dates. Measurements from 7 ewes over 2 breeding seasons were taken and equations were developed relating gestational age to these measurements. The equations were then used to predict lambing dates from later measurements, with predictions usually within 2 weeks of actual dates. While useful, the study was limited by small sample size and challenges in late-term measurements. Larger, more frequent studies in different breeds could improve fetal measurement techniques.

1. Estimation of Fetal Development
in Cheviot Ewes with
Ultrasonography
By Susanna Edwards
Project facilitation from Dr. Craig Darroch

2. Introduction: Lambing
• Lambing date prediction is important because it
helps producers plan farm management techniques.
▫ Planning nutrition,
vaccines, deworming,
pasture rotation,
and other management
for pregnant ewes
▫ Separating pregnant ewes
from nonpregnant ewes
and those at different
stages of pregnancy
▫ Setting up lambing pens
in time for lambs’ arrival
https://www.farmersjournal.ie/labour-saving-safety-tip-at-lambing-time-200165
Lambing pens such as these keep the
mother and her newborns close for a
few days so they can bond.

3. Introduction: Ultrasonography
• Ultrasonography can
be used to quantify
the size of various
fetal body parts
• Bone appears as
bright white on an
ultrasound scan
• Ovine gestation is
147 days on average An ultrasound scan of an unborn lamb’s skull

4. Previous research
• Pregnancy can be detected starting at approximately
day 24 (Garcia et al., 1993).
• Crown-rump length and biparietal diameter are
considered effective and reliable measurements for
estimation of gestational age in lamb fetuses (James
et al., 2015; Gonzalez de Bulnes et al., 1998).
Crown-rump length is the
distance from the nose to the rear.
Biparietal diameter is the width of
the skull (from one side of the
parietal bone to the other).

5. Objective
• The purpose of this study was to correlate the
biparietal diameters and crown-rump lengths of
Cheviot fetuses to gestational age in an effort to
predict lambing dates for this breed.

6. Materials: Animals
• Three mature Cheviot ewes were bred and
measured in the 2016-2017 season, and four
were bred and measured in the 2017-2018
season.
▫ Ewes were cared for using
routine farm management
procedures at the UT Martin
Teaching Farm.
A ewe at the UT Martin Teaching Farm

7. Materials: Equipment
• A marking harness was fitted to
the ram.
▫ The harness left a colored spot
on each ewe after she was bred.
• Transabdominal
ultrasonography was performed
using an ExaGo portable
ultrasound unit with a C360A
probe (ECM, France).
▫ Settings were usually set to 80
gain, 2.50 MHz frequency, 100%
power, and 60dB dynamic. The portable ultrasound
machine and probe used in this
study

8. Methods
• Breeding dates were recorded during the fall
breeding season by using a marking harness on
the ram, and lambing dates were recorded in the
spring.
• Imaging days were
scheduled approximately
six weeks apart.
• On each day of imaging,
ewes were restrained on
a standard sheep
trimming stand. Sheep usually were cooperative while
standing on the trimming stand.

9. Methods cont.
• Crown-rump length and biparietal diameter
were measured on each fetus when possible.
▫ Crown-rump length was measured until 65 days of
gestation.
▫ Biparietal diameter was measured starting at 35
days of gestation.
• When possible, two or three measurements were
taken on each fetus and averaged together.
• If twins were present, measurements were taken
for each fetus.

10. Results: Graphs
0
20
40
60
80
100
120
140
0 20 40 60 80
crown-rumplength(mm)
gestational age (days)
Figure 1: Crown-Rump
Length Development
0
10
20
30
40
50
60
70
0 50 100 150 200
biparietaldiameter(mm)
gestational age (days)
Figure 2: Biparietal
Diameter Development

11. Results: Equations
• Crown-Rump Length Development
▫ crown-rump length = 2.096(gestational age) -
40.33
▫ R2 value of 0.688
▫ Statistically significant correlation (p<0.05)
• Biparietal Diameter Development
▫ biparietal diameter = 0.388(gestational age) +
1.074
▫ R2 value of 0.790
▫ Statistically significant correlation (p<0.05)

12. Results: Application
• Equations were tested on the three sheep that
lambed in spring 2018.
• Using an assumed gestational length of 147 days,
the lambing date was predicted from each
measurement for each fetus and compared to the
actual birth date.

13. Results: Prediction Tables
Table 1: Lambing Date Prediction Using
Biparietal Diameter
Ewe
Date
measured
Biparietal
diameter
measurement
predicted
lambing date
actual
lambing
date
30 12/2/2017 20.2 3/9/2018 2/24/2018
12/2/2017 21.1 3/7/2018
1/7/2018 42.7 2/15/2018
1/7/2018 43.1 2/14/2018
31 12/2/2017 14.8 3/23/2018 3/19/2018
1/7/2018 32.9 3/12/2018
2/10/2018 55.8 2/15/2018
33 12/2/2017 28.4 2/16/2018 2/26/2018
12/2/2017 29.4 2/13/2018
1/7/2018 44.3 2/11/2018
1/7/2018 44.5 2/11/2018
2/10/2018 57.5 2/11/2018
2/10/2018 54.6 2/19/2018
Table 2: Lambing Date Prediction Using
Crown-Rump Length
Ewe
Date
measured
CR
Measurement
predicted
lambing date
actual
lambing
date
30 10/28/2017 11.5 2/27/2018 2/24/2018
12/2/2017 48.1 3/16/2018
12/2/2017 75.4 3/3/2018
31 12/2/2017 61.5 3/10/2018 3/19/2018
33 10/28/2017 12.7 2/26/2018 2/26/2018
12/2/2017 132.8 2/4/2018
12/2/2017 105.4 2/17/2018

14. Discussion: Limitations
• Inconsistencies in measurements could be due
to a number of challenges.
▫ Ewe #32 miscarried.
▫ The breeding dates from fall 2016 and from Ewe
#31 in fall 2017 were estimated but the other
breeding dates were precise.
▫ When the fetuses became too large to fit on the
ultrasound screen or were positioned oddly,
crown-rump length had to be measured in two
parts, which introduced much variation.

15. Discussion: Measurement Timing
• Studies have shown that it is possible to measure crown-
rump length up to about day 48 via transabdominal
ultrasonography (James, 2015) and transrectal
ultrasonography (Gonzalez de Bulnes et al., 1998).
• Studies have also shown that it is possible to measure
biparietal diameter transabdominally from about day 45
to 100 (James et al., 2015) or day 46 to 63 (Petrujkic et
al., 2016) and transrectally from day 32-91 (Gonzalez de
Bulnes et al., 1998).
https://www.dhgate.com/product/ultrasound-scanner-2-5-7-5mhz-convex-array/374041004.html
Example of a
transabdominal
probe (like that
used in
this study)
Example of a
transrectal probe
(used commonly
in other studies)

16. Discussion: Measurement Timing
• This study found these ranges to be approximately
correct.
▫ Crown-rump length was
measured up through 65
days of gestation, but the
last measurements were
not very reliable because
many of them had to be
taken in two parts.
▫ Likewise, many biparietal
diameter measurements
could not be obtained
toward the end of gestation
because of difficult fetal
positioning.
For instance, this crown-rump length
measurement had to be taken in two
parts because the fetus was turned.
rump
crown
shoulder

17. Future Research
• Future research would most benefit from a
larger sample of pregnant ewes and more
frequent measurements.
• Research should also be done for other breeds of
sheep, as prenatal developmental rates may
vary.
The Cheviot breed of
sheep was used for
this study.

18. Works Cited
• Petrujkic, B. K., Cojkic, A., Petrujkic, K., Jeremic, I., Masulovic, D.,
Dimitrijevic, V., . . . Beier, R. C. (2016). Transabdominal and
transrectal ultrasonography of fetuses in Wurttemberg ewes:
Correlation with gestational age. Animal Science Journal, 87(2),
197-201. doi:10.111/asj.12421
• Gonzalez de Bulnes, A., Santiago Moreno, J., & Lopez Sebastian, A.
(1998). Estimation of fetal development in Manchega dairy ewes by
transrectal ultrasonographic measurements. Small Ruminant
Research, 27, 243-250
• James, A. A., Chom, N. D., Fadason, S. T., Andrew, A., & Emmanuel,
E. G. (2015). Ultrasonographic Determination of Gestational Age in
Yankasa Ewes. Journal of Veterinary Advances, 5(11), 1169-1175.
doi:10.5455/jva.20151125104035
• Garcia, A., Neary, M. K., Kelly, G. R., & Pierson, R. A. (1993).
Accuracy of ultrasonography in early pregnancy diagnosis in the
ewe. Theriogenology, 39, 847-861.